DEM-ADS82xE ® EVALUATION FIXTURE FEATURES DESCRIPTION ● PROVIDES FAST AND EASY PERFORMANCE TESTING FOR ADS822/823/824 The DEM-ADS82xE evaluation fixture is designed for ease of use when evaluating the 10-bit high speed analog-to-digital converter ADS822, ADS823 and ADS824. The three converter feature different sampling rates, 40Msps, 60Msps and 70Msps respectively, and each model is available by its individual demonstration board. Because of its flexible design the user can evaluate the converter in many different configurations: either with dc-coupled or ac-coupled input, single-ended or differential inputs. The data output of the ADS82x converter are decoupled from the connector by CMOS octal logic buffers. ● AC- OR DC-COUPLED INPUTS ● SINGLE-ENDED OR DIFFERENTIAL INPUT CONFIGURATION ● EXTERNAL REFERENCE OPTION International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111 Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 © 1998 Burr-Brown Corporation LI-509 Printed in U.S.A. January, 1998 Transformer Coupled The demonstration board provides the option to evaluate the A/D converter with differential signal inputs. Here, a RFtransformer is used to convert the single-ended input signal applied to SMA connector J3 into a differential signal. The following steps have to be done to prepare the board: INITIAL CONFIGURATION By using solder switches and resistor placements the demonstration board, DEM-ADS82xE, can be set up in a variety of configurations to accommodate a specific mode of operation. Before starting evaluation, the user should decide on the configuration and make the appropriate connections or changes. The demo board comes with following factory set configuration: • Remove resistors R19, R20 and R22, R23. • Remove C41 and replace with a 47pF capacitor. • OPA681 is set for a non-inverting configuration with a gain of +2V/V (R9 = R10 = 402Ω). R8, R12, R13, R15, C37 are not assembled. • Remove R16, C39 (C38). • Install R18 and R21, typically 22Ω. • Install RF-transformer (U5). The model TT1-6, for example, is a 1:1 wideband RF-transformer manufactured by ‘Mini-Circuits’. The layout is prepared for the ‘KK81’ case style (surface mount). Note to add a proper termination resistor depending on the selected transformer model. • With capacitor C39 the output of the driver op amp OPA681 is ac-coupled to the converter input. • The converter is set to operate with the internal reference—solder switch JP4 is closed. • The full-scale input range is set to 2Vp-p. The solder switch JP3 is open. • Install R17. Consider to use a 0.1µF capacitor to block the DC path in the case the input signal carries a DC voltage. • The required common-mode voltage to bias the input of the ADS82x is derived from the internal top- and bottom references by R19 and R20 and applied to the signal input of the ADS82x, pin 25 (U1). This differential input configuration can be operated with external references as well. CLOCK The evaluation board DEM-ADS82xE requires an external clock applied at SMA connector J1. This input represents a 50Ω input to the source. In order to preserve the specified performance of the ADS82x converter the clock source should feature a very low jitter. This is particularly important if the converter is to be evaluated in an undersampling condition. • The bias for the complementary input of ADS82x is developed in a similar fashion using R22 and R23. POWER SUPPLY The evaluation board typically operates with a ±5V power supply. This ±5V supply, applied at connector P1, is the supply for the analog front end and is separated from the converter supply. The ADS82x is powered with a +5V supply through connector P2. By using the negative supply for the driving op amp the applied input signal can be a ground referenced signal with a bipolar swing and does not need to be level shifted. However, the input driver, OPA681, can be set to operate with a single +5V supply as well. EXTERNAL REFERENCE The ADS82x converter can be operated with an external reference. For this solder switch JP4 must be opened disabling the internal references. Close solder switches JP5 and JP6 and apply the external reference voltage at connector P3. Refer to the A/D converter data sheet for the recommended reference voltage ranges. SIGNAL INPUT DC-Coupled The standard configuration of the evaluation board uses the high-speed op amp OPA681, a current-feedback type op amp that features low distortion. In order to implement level shifting for the dc-coupled circuit configuration op amp U4 needs to be re-configured for inverting mode. For this, remove R9 and install R8. The level shifting voltage is derived from the +5V supply and applied to the noninverting input. To generate the correct DC-voltage calculate appropriate values for resistors R12 and R13 an close solder switch JP8. Note that in this configuration the input impedance to he board is also determined by the input resistor, R8, and an appropriate termination resistor (R7) value should be selected. The selected reference voltage determines the full-scale input signal range of the converter. DIGITAL OUTPUT DRIVER SUPPLY, VDRV The ADS82x converter feature a dedicated supply pin for the output logic drivers, VDRV, which is not internally connected to the other supply pins. This allows the ADS82x to be interfaced to either +3V or +5V logic. On the evaluation board the VDRV supply available at connector P2 is shorted to the analog +5V supply with the 0Ω resistor, R25. DATA OUTPUT The data output is provided at CMOS logic levels. The ADS82x converter use straight offset binary coding. The data output pins of the converter are buffered from the I/O connector, CN1, by two CMOS octal buffer (FCT541). To change the input full-scale range from 2Vp-p to 1Vp-p close solder switch JP3. ® DEM-ADS82xE 2 FIGURE 1. Circuit Schematic DEM-ADS82xE. 3 DEM-ADS82xE ® AIN J2 R7 49.9Ω C4 100µF + C3 0.1µF –5V 3 C37(1) 0.1µF R12(1) R11 0Ω R8(1) R9 402Ω 2 +5V 1 R10 402Ω R17(1) JP8 4 5 + C31(1) 0.1µF 6 C35(1) 0.1µF + +5V C30 C32(1) 2.2µF –5V 2.2µF + C29 0.1µF 3 8 OPA681U C33 0.1µF 7 2 + 3 (1) R14 49.9Ω VDRV R15 4 3 6 5 TT1-6 2 1 C8 100µF + C7 0.1µF U5(1) C34 +5V C36(1) 2.2µF 2.2µF (1) J3 DIFF. IN R13(1) C2 100µF + C1 0.1µF P1 R18 22Ω (1) R21 22Ω (1) R25 0Ω 2 C39 0.1µF R16(1) 0Ω C38 2.2µF + (1) VDD 1 + C6 100µF C5 0.1µF P2 JP5 VDRV 2 JP4 JP3 C24 + 2.2µF C22 + 2.2µF VDD C20 + 2.2µF C18 + 2.2µF C16 2.2µF + C14 + 2.2µF 1 REFT VDD C12 + 2.2µF C10 2.2µF C40 47pF REFT R24(1) R19 1.62kΩ R22 1.62kΩ R20 1.62kΩ R23 1.62kΩ JP6 REFB REFB 3 C23 0.1µF 28 C21 0.1µF 27 26 25 C41 0.1µF 24 C19 0.1µF 21 C17 0.1µF 22 C15 0.1µF 21 C13 0.1µF 20 C11 0.1µF 19 18 17 16 C9 0.1µF 15 VDRV VDD GND IN IN CM REFT ByT ByB REFB INT/EXT RSEL GND +VS OE PD CLK GND (MSB) B1 B2 B3 B4 B5 B6 B7 B8 B9 (LSB) B10 U1 ADS82xE 1 07 06 05 04 03 02 01 00 D7 D6 D5 D4 D3 D2 D1 D0 OEB OEA 20 O7 O6 O5 O4 O3 O2 O1 O0 11 12 13 14 15 16 17 18 GND 10 VCC 17 1 3 5 7 9 11 13 15 2 4 6 8 10 12 14 16 18 20 21 22 19 33 23 24 25 26 11 C25 0.1µF C27 0.1µF 27 28 29 30 31 32 34 35 36 37 38 40 39 12 13 14 15 16 17 18 GND 10 VCC U2 IDT74FCT541T D7 D6 D5 D4 D3 D2 D1 D0 OEB OEA 20 L2(1) L1 U3 IDT74FCT541T +5V VDD NOTE: (1) Part not assembled. 9 7 6 5 4 3 2 19 1 9 8 7 6 5 4 3 2 19 1 2 R4 10kΩ R3 10kΩ R6 10kΩ R5 10kΩ VDD 8 JP1 JP2 R1 49.9Ω 3 4 5 6 7 8 9 12 13 14 ADS82xE EVALUATION FIXTURE P3(1) J1 Clock Input CN1 OE CN1 (MSB) B1 CN1 B2 CN1 B3 CN1 B4 CN1 B5 CN1 B6 CN1B7 CN1 B8 CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1GND CN1 GND CN1 B9 CN1 (LSB) B10 CN1 CLK CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1 GND CN1GND CN1 GND treated like an analog component. Therefore the demo board has one consistent ground plane. Keep in mind that this approach may not necessarily yield optimum performance results when designing the ADS82x into different individual applications. In any case, thoroughly bypassing the power supply and reference pins of the converter, as demonstrated on the evaluation board, is strongly recommended. PC-BOARD LAYOUT The DEM-ADS82xE demo board consists of a four layer PC board. To achieve the highest level of performance surface mount components are used wherever possible. This reduces the trace length and minimizes the effects of parasitic capacitance and inductance. The analog-to-digital converter is FIGURE 2. Top Layer (Component Side) with Silk-Screen. ORDERING INFORMATION PRODUCT ANALOG-TO-DIGITAL CONVERTER DEM-ADS822E ADS822E, 10-Bit 40Msps DEM-ADS823E ADS823E, 10-Bit 60Msps DEM-ADS824E ADS824E, 10-Bit 70Msps ® DEM-ADS82xE 4 FIGURE 3. Ground Plane. FIGURE 4. Power Plane. ® 5 DEM-ADS82xE FIGURE 5. Bottom Layer with Silk-Screen. COMPONENT LIST REFERENCE QTY COMPONENT DESCRIPTION MANUFACTURER U1 1 ADS82xE High-Speed ADC, 28-Pin SSOP Burr-Brown U2, U3 2 74FCT541 5V Octal Buffer, 20-Pin SOIC IDT U4 1 OPA681U Wideband, Single Op Amp, SO-8 Burr-Brown R11, 25, L1 3 CRCW0805ZEROF 0Ω, MF 0805 Chip Resistor, 1% Dale R1, 7, 14 3 CRCW080549R9F 49.9Ω, MF 0805 Chip Resistor, 1% Dale R9, 10 2 CRCW08054020F 402Ω, MF 0805 Chip Resistor, 1% Dale R19, 20, 22, 23 4 CRCW08054751F 1.62Ω, MF 0805 Chip Resistor, 1% Dale R3, 4, 5, 6 4 CRCW08051002F 10Ω, MF 0805 Chip Resistor, 1% Dale R8, 12, 13, 15, 16, 17, 18, 21, 24 9 C2, 4, 6, 8 C10, 12, 14, 16, 18, 20, 22, 24, 30, 34 Open, Use Depends on Configuration 4 ECE-V1CV101SR 100µF/16V, Surface Mount Polar. Alu Cap. Panasonic (Digi-Key) 10 TAJR225006 2.2µF/10V, 3216 Tantalum Capacitor AVX C1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 33, 39, 41 18 08055C104KAT 0.1µF/50V X7R 0805 Ceramic Capacitor AVX C40 1 08055C470KAT 47pF/50V NP0 0805 Ceramic Capacitor AVX C31, 32, 35, 36, 37, 38 6 Open, Use Depends on Configuration — P1, P2 2 ED555/3DS 3-Pin Term Block On-Shore Technology CN1 1 IDH-40LP-S3-TG 20 x 2 Dual-Row Shrouded Header Robinson-Nugent EF Johnson J1, J2 2 142-0701-201 Straight SMA PCB Connector 4 1-SJ5003-0-N Rubber Feet, Black, 0.44 x 0.2 Digi-Key 1 PCB A2403 PC Board A2403, Rev. B Burr-Brown ® DEM-ADS82xE 6